Telephone trunking system.



I T. G. MARTW; TELEPHONE mumunre SYSTEM.

Patented 00t." 17,1 916.

[mum

5 SHEETS-SHEET l.

APPL ICATION FILED SEPT. 289190].

T. G. MARTIN.

' TELEPHONE TRUNKING SYSTEM,

' 1 APPLICATION FILEDASEPTJB. 19oz.

1,201,600. Patented Oct. 17,1916.

5 SHEET SSHEET 2.

Us ME T. a. MARTIN. TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED SEPT. 23, I907.

Patented Oct. 17, 1916.

5 SHEETS-SHEET 4 T. G. MARTIN. v TELEPHONE TRUNKlNG SYSTEM. APPLICATION FILED SEPT- Z, 1907.

1,201,600. Patented Oct. 17,1916;

5 SHEETS-SHEET 5.

7 l j T 5 55 513 3%9 M59 255 5055726 e I E M )5 rafg z i fzz transits? gossips,

TALBOT G. MABTI N, OF CHICAGO, ILLINOIS, ASSIGNOE, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC COMPANY, A CORPORATION OF ILLINOIS.

TELEPHONE TRUI'IKING SYSTEM.

Leoneoo,

Specification of Letters Patent.

Patented Oct. 1?,1918.

. Application filed. September 28,1907. Serial No. 394,984..

resident of Chicago, Cook county, Illinois,

5 have invented a certain new and useful Improvement in Telephone Trunking; Systems, of which the following is a specification.

My invention relates to telephone systems in general, but more particularly to auto .matic or semi-automatic telephone exchange systems, and especially to systems in which automatic or semi-automatic trunking service may be required between two or more of granted April 25, 1916, inasmuch as Ihave herein disclosed an improved arrangement of rotary connectors-that s to say, contomatically select idle trunk-lines, the rotary or automatic trunk-selecting feature being limited or confined to a certain level, and the other levels thereof being employed for-ordinary service-that is to say, for completing the final connections directly with the lines of the called subscribers.

lvly present invention, however, conteniplates broadly a combined connector and repeater, with provisions for bringing: the repeater mechanism into play only when the connector is operated at a certainlevel; and it also contemplates broadly an automatic connector which is rotary or trunk-selecting in character at a certainlevel only, and which at this level is also adapted to have itsline relays serve as part of the mechanism for then repeating or-relaying switchoperating; impulses over the automatically selected idle trunk-line.

As herein disclosed, present invention and improvements are embodied in a system comprising a main automatic exchange and a branch automatic exchange to nectors 'whichare adapted to rotate and augether by two-way trunk-lines; the equipment of the main automatic exchange including first and second selectors and connectors for enabling thesubscribers thereof 'to call each other automatically; the equipment of the branch exchange including subscribersnon numerical trunking switches and connectors, without any intermediate selectors, whereby the subscribers thereof can call each other automatically. Furthermore, as herein disclosed, there are two-way trunk-lines between the two exchanges, each trunk-line terminating in a first-selector and a repeater at the main exchange, as well as in second-selector bank terminals; and at the v branch exchange each of said trunk-lines terminates in a non-numerical trunking; switch, as well as in multiple terminals of the connectors of this exchange. The said connectors of the branch exchange are adapted for use in giving ordinary service between the subscribers thereof, and are also adapted, when raised to a certain level, to rotate automatically and thereby automatically select an idle trunk leading to the main exchange; and these connectors which are,

so to speak, rotary or trunlcselecting when operated-at a certain level,are also adapted to serve as repeaters, both the trunk-selecting and repeating functions of these connectors being brought about, for example, by raising any connector to the tenth level, all 9 other levels of the bank terminals of the connectors being reserved for ordinary servicethat is to, say, for making the final con nections directly with the lines of called subscribers.

With such arrangement any subscriber at the branchexchange can call any other subscriber thereof, and can also automatically call any subscriber at the main exchange, inasmuch as the connector which seizes an idle trunk-line will then serve as a repeater at the main exchange to a certain level the Ceiling subscriber thereof can obtain connection with the repeater of an idle trunk-line leading to the branch exchange, and said repeater can then be employed for controlling the non-numerical trunking switch at the other end of the said trunk-line, as well as for, controlling the connector necessarily. brought into use at the branch exchange for completing connection to and finding the line of the called subscriber thereof. Means areprovided, as will hereinafter more fully appear, whereby when one of said trunklines is used in one direction, no subscriber .caninterfere with such use by attempting to use-1t 1n the same direction, or by attemptlines .=leading.to:;the branch exchange.

The nature and advantages of my invention will, however, hereinafter more fully appear.

1n the accompanying drawings Figure 1 represents diagrammatically a sub-central or private branch exchange in which the substation A is-shownas having operated its line switch 0 and the connector H to establish connection with the substation A, which latter is allotted to the line switch C, in va system embodying the principles of my invention. In Fig. 2 there is shown diagrammatically a central station switching apparatus in connection with which I have elected .to explain my invention.' The first selector switches E and E are of the :type

disclosed in United'States Patent No. 815,321, granted .March 13, 1906, to Keith, Erickson and Erickson, while the second-selector F sa modified form of the selector shown in' said patent. The connector switch shown at 1 is of'the general type shown in United States Patent No. 815,176, granted March -13,' 1966, .to Keith, Erickson and Erickson.

Atd is diagrammatically represented a repeater, and at A a substation like the substations A and A. All of the switches E, E, if, '1 and .J are allotted to the main or In Fig. '3 there is represented another first-selector E with its allotted substation A of the main central station. Fi.g. 4 is anenlarged view of the line switchc. and its allotted master swatch D.

Fig. 5 is a detail View of the bank 0 of the master switch D. Figs. 6, 7, 8, 9,10, 11 and 12 are detail views showing the various po-v sitions of the impulse springs of the substation A.

Figs. 1, 2 and 3 taken together represent the system as awhole, comprising the subscribers equipment at substation A of the private branch or sub-central exchange, and the subscribers equipment at substation A of the main or central exchange.

The substations are all alike and maybe of any suitable or approved type. The substation A, for example, comprises a receiver 2, a switch-hook 3 for controlling the substation circuits, which controlling operations are accomplishedthrough the medium of any suitable means, such as the cam arms 4,

5 and 6. As the switch-hook is lowered the cam-arm 4 momentarily presses the release springs 7, 8 and 9 into engagement, whereby the substation lineconductors may be groundedsimultaneously, if the springs 18 and 19 are in contact, for the purpose of releasing the switching apparatus at the central station. When the switch-hook is down the cam-arm 5 engages the spring 10, thereby bridging the ringer 11 in series with the condenser 12 across the line. Furthermore, when the switch-hook is down the said cam-arm 5 disengages the springs 13 and 14, thus breaking the local circuit which includes in series the primary winding 15, transmitter 16 and local battery 17. The substation ground circuit is normally broken between the ground springs 18 and 19 by the cam arm 6; but when the said I springs are together ground is provided to the ground post 20 and to the release spring 7 as is usual in telephone equipments of this type. The said substation comprises the usual induction-coil 21 having the primary winding 15 and secondary winding 22. Being an automatic substation it is provided with the vertical and rotary impulse springs 23 and 24-. Said substation is, of course,

provided with a dial (not shown) which issecured to the shaft 25, together with the locking dog 26. Furthermore, there is a locking cam 27 that locks the dog 26 while the receiver is on the switch-hook to prevent a rotation of the dial. For operating the impulse springs 23 and 24 the substation is provided with an impulse wheel 28 that is secured to the shaft, which impulse wheel. carries on its periphery the so-ealled vertical impulse teeth 29 and one rotary impulse tooth 80. The said impulse teeth are so arranged that when the dial is drawn down the impulse spring 28 is not carried into contact with the ground post 20, but only as the dial returns, whereby the vertical impulse spring 23 is pressed onto the said ground. post'2O by one or more of the vertical impulse teeth, and after the latter have completed their work the rotary imulsetooth in a similar manner crates theiot'ary impulse spring 24. In this opertion the subscribe'rs vertical line conductor '31 is first given a number of ground impulsesgiand then the rotary line conductor 32-is-given one ground impulse. It will be springs 33 and 34 to separate, thus prevent ing the impulses that are delivered to either line conductor from passing to the other. The vertical impulse spring 23 is provided with an oblique projection or lug 39 (see Figs. 6 to 12, inclusive) on the under side of which the vertical impulse teeth 29 are adapted to engage for intermittently driving: the spring 23 onto the ground post 20. The otary impulse spring 24 is provided with somewhat similar mechanism for driving the said rotary spring onto the ground post once when the dial is rotated in one direction, and once when rotated in the opposite direction. The said rotary impulse spring 24 has on its under side a V-shaped member 40 having two sides 0 and d, and there is, in addition, an auxiliary spring 41 which works inconjunction with the said V-shaped member. As shown more clearly in Fig. 6, the auxiliary spring 41 is provided with a lower curved part 6 having the rear section 42 curving outwardly, asshown in Figs. 7, 8, 9, 10, 11 and- 12.. The front section 43 of said member 6 is designed to fall just behind the apex of the V-shaped member 40, so that the rotary impulse tooth.30, when moved in the direction indicated by the arrowin Fig. 7, will pass onto the curved member 6, thus pressing the rotary impulse spring 24 onto the ground post 20 for a comparatively long time, as shown in Fig. 8, thus sending a coin paratively long impulse to the line.

As the impulse wheel advances, the vertical impulse teeth 29 approach the lug 39 of the vertical impulse spring 23 (Fig. 8), and eventually thefirst tooth j, that meets the lug 39 clears the said lug, as shown in Fig. 9, but not until after the rotary impulse tooth 30 clears the curved member a. As the inipulse wheel continues to advance in the direction of the arrow (Fig. 9), the succeeding impulse teeth 29. will clear the projection 39,

as shown in Fig. 10. Then when the impulse wheel is released, first the vertical impulsespring 23 is carried into engagement with the ground post 20 by the vertical impulse teeth previously cleared, as indicated in Fig.

11' and as the im ulse wheel nears its nornull position the rotary impulse tooth 30 passes under the curved membere of the auxiliary spring, 41 (Fig. 12), en aging the V-shaped member 40 directly and or a short time only, sendin the ordinary impulse to the line 82 throng the med um of the rotary impulse spring 24, after which the said membcr40 is cleared or disengaged, as shown in Fig. 7. The operations as thus described are repeated each time that the dial is operated, and the number of impulses produced through the medium of the vertical impulse spring 23 are accurately and definitely determined at each operation of the dial by the finger-hole which the subscriber selects there on. The means whereby the subscriber may signal the called subscriber comprises the push-button s iiring 35 which normally engages the contact point 86; but when the button 37 is pressed the spring 85 engages the contact point'38, whereby the vertical line conductor 31 may be grounded. As shown in lug. 4, the individual switch comprises a plunger 44, plungerarm 45, bridgecut-elf relay 46, trip magnet 47 and switchrelease magnet 48. all of which are built about a switch-base or frame (not shown) of any suitable or approved design. The said switch-release magnet is-provided with an armature 49 that is pivoted ona pin 50 which rises from the .base of the switch. The said armature carries pivotally secured on its end a second armature 51 that is controlled by the trip magnet 47. The pin 52 about which the armature 51 oscillates is carried on the end of the armature 49. The

plunger 44 is pivotally secured by the pin 53 to the plunger arm 45, which latter is in turn pivoted to a pin 54 that rises from the switch frame. The lug 55 is stamped out of the side cfthe frame and is provided as a stop or rest for the armature 49. Upon the armature 51 is secured the catch 56which is adapted to engage the plate 57 on the end of the plunger arm 45. Furthermore, the said line switch is provided with a bank of terminals, usually ten in number, only one of which is shown at Q in Fig. 4. As shown, the said terminal. Q is turned from its true position with respect to the swing 'of the plunger 44, and the bushing '62 is correspondingly turned, all for the purpose of making the illustration clearer.- The terminal Q. comprises the springs 63 and 64, 65 and 66, (l? and 68, and 69 and 70. The said springs are normally disconnected from each above-mentioned order when the plunger 44 operates. When the plunger 44 is in locked engagement with the plunger shaft 60, the notch 61 is in engagement with the flange or web of the shaft 60, and when in sliding engagement the hub rests in the position shown by the dotted lines in Fig. 4that is, when the plunger shaft is operated the plunger 44 not carried along with the locked plungers,

but remains in the dotted position, the plunger shaft sliding upon the end 59. The general operation of the switch is as follows: The tiip l'l'litgl l it 4? is energized by a pie hinmsry'mip and the armature title at its naoneoo arm 45, and the said plunger arm 45, owing to the tension of the spring 58, moves about the pin 54 and thrusts the plunger 44 into the bank terminal Q (shown in Fig. 4), and

when the trip magnet again de'elnergizes, the

trip armature 51 falls against the end of the plunger arm 45.

The switch is restored when the release magnet 48 becomes energized, whereby the armature 49 is attracted, and accordingly the trip armature 51 is moved upwardly until the catch 56 slides over the end 57; then when the release magnet 48 becomes deenergized the armature 49 returns to normal position by the action of the spring 58, since the plate 56 is now locked on top of the plate 57, and

the armature ,49 remains at rest against the Furthermore, since the plunger stop 55. arm 45 is now in engagement with the armature 51, the said plunger arm is also moved about the pin 54, whereby the plunger 44 is moved from the terminal Q. Also, since the plunger shaft has advanced one step, the hub 59 of the plunger 44 comes to rest in the position shown by the dotted line in Fig. 4, in sliding engagement with the plunger shaft 60; and as the said plunger shaft advances each time an idle trunk is seized, the plunger 44 is not advanced, but remains in this position opposite the trunk terminal from which it has just disengaged, since the slot (31 is not in engagement with the plunger shaft 60. After all the trunk lines have been successively seized, and the shaft 60 is released from its last position, said shaft then starts toward the starting point and picks up the plunger 44, when the saddle of said shaft, over which the slot 61 normally rides, arrives at the position at which the plunger 44 was originally releasedthat is, the plunger passes into locked engagement with the shaft when the slot 61 slips over the saddle of said shaft. From thence on the plunger 44 is carried by the shaft 60 until it is again released when another call is made. But if, after the plunger is released, and before the shaft 60 returns to pick up said plunger, the switch C is again operated, the plunger 44 again engages the same terminal Q. The

, master switch D, which may be of any suitable or approved type, is provided for operating the plunger shaft 60, and for controlling certain circuits that will be disclosed hereinafter. It comprises the following details: A motor magnet 71 for operating the ratchet wheel 72, which latter is designed for operating the plungershaft 60, and a differential relay 73 for controlling the energizing circuit of the motor magnet 71. The said master switch also has a bank 0 comprising a plurality of individual Contact segments a, and a. new man metalli segment 74, as strew in Fig. 4. The wiper 75 is adapted to remain in constant engagement with the bank 0, and to maintain some one of the segments a,

in electrical connection with the common segment 74. The wiper 75 is operated in a step-by-step manner by the ratchet wheel 72, through the medium of a cam member 76 rigidly secured to the said wiper 75 and adapted to successively engage the pins 77 78, .7 9-.and 80 upon the said ratchet wheel 72. The motor magnet 71 is provided with an armature 81 upon the end of which there is suitably secured a pawl 82. Each time that the said magnet is energized the pawl 82 engages the ratchet wheel 72, advancing the latter one step. It will be seen, therefore, that as the ratchet wheel 72 advances, the wiper 75 advances step by step from right to left, and when the pin 77, for instance, clears the cam 76 the retracting spring 83 restores the Wiper 75 to its first position at the right of the bank 0 and in engagement with the first segment 84. The said motor magnet 71 is provided with a couple of interrupter springs 85 and 86 that are included in the energizing circuit of the said motor magnet, which energizing circuit also comprises the springs 87 and 88 controlled by the differential relay 7 3. Therefore, whenever the differential relay 73 is energized the springs 87 and 88 are pressed into contact, and the motor magnet 71 operates step by step as long as the differential relay 7 3 remains energized. Furthermore, it is assumed that the terminal Q of the line switch G is the first terminal of the line switch bank. lVhile in normal locked engagement with the shaft 60 the plunger 44 is retained in front of said terminal by the plunger shaft 60 as long as the master switch wiper 75 is in engagement with the bank segment 84; but as the motor magnet 71 advances the'wiper 75 onto the second segment 89, the said plunger and all idle plungers similarly engaging the shaft 60 are carried opposite the next terminal of the line switch bank. bank O (Fig. 5) comprises the individual segments a separated from the common se ment 74 by the insulating strip 116.

It will be seen that after the wiper 75 passes over the segments from right to left and engages the last segment 117, then on the next step the wiper 75 passes from the The master switch" this extreme position to the other the upper part of the wiper 75 slides on the insulated member 118. f This provision is made in order that the individual segments a. may not be brought into contact with the common segments 74, whereby some interference with the successful operations of the master switch might be eXperienced. .It should 'be noted that-in each switch bankall of the errinssfifi; arerermariently animated and Y X may be made of one connnon piece. The

springs 64, however, are individual-that is, there is one separate and distinct spring'for every terminal Q, there being ten in the bank. The springs 65,- 67, 68 and 69, like the springs 63, are also common, and the springs 66 and 70, like the springs 64:, are individual. 'Eor every bank terminal Q there isa trunk-line of three conductors 90-, 91 andv92 leading to a connector switch; and there is also a normal trunk-line comprising the conductors 93, 94,- and 95 leading to the connector switch banks. The subscribers line conductors 31 and 32 terminate in the springs'63 and 65 which, as has been stated, are common springs. \Vhen the subscriber operates the line switch C, and the plunger 44 engages the terminal Q, the subscribers line conductors 31 and 32 are extended to the vertical and rotary trunk conductors 90 and 91, thence to the connector switch H. I

.The connector switch H is an improved form of the; connector switch described in ,United States Patent No. 815,176. For instance,'theconnector switch shaft carries theline wipers 96 and 97 and the private wiper 98. The connector switch is also controlled by the calling subscriber through the 'medium of the vertical and rotary line relays 99 and 100. The vertical line relay 99 directly controls the vertical magnet 101 and also the rotary magnet 102. The function of the vertical magnet 101 is to give the shaft and shaft wipers a vertical motion, and the rotary magnet 102 imparts to the shaft and shaft wipers a rotary or circular 100 conjointly.

motion. The rotary line relay 100 controls the private magnet 103, which latter, under certain conditions, controls in turn the vertical and rotary magnets 101 and 102, the

" release magnet 10 1, and also the side switch wipers 105, 106, 107, 108 and 109. The side switch of the connector, like the side switch oi" the selector, has a normal or first position, a second position and a third position. V I

by the vertical and rotary line relays 99 and By the use of the condensei-s 110 and 111 the connector circuit is divided into two sections. The relay 112 is provided for bridging the ringer generator K across the terminals of the called line. The relay 113, upon energizing, operates to disconnect'thevertical and rotary line relay springs-196 and 207, respectively, from the side switch wiper 107 and private magnet 103, and to connect them instead to the shaft wipers'96 and 97, whereby the succeeding impulses from the connector vertical and rotary line relays are'repeated to the conductors, with which the wipers may be in contact. Furthermore, it should be noted that the release mechanism of the connector H operates like that of the selector switch disclosed in said selector patent, insteadof no release magnet 101 is also controlled tacts of this connector are shown, which are as follows: The bank contacts with which the wipers 96, 97 and 98 are shown in engagement are-the tenth set of contacts of the second level, while the remaining bank contacts shown in connection with said wipers 96, 97 and 98, but a little above them, arethe first, second, third and fourth set of bank contacts of the tenth level. -()f these sets in the tenth level the first private bank contact 210 is shown grounded, while the fourthprivatc bank contact is shown insulated. The selectors E, E and E shown in Figs. 2 and 3 are of the type disclosed in said selector'patent. The selector switch vE is provided with a vertical magnet 127 and a rotary magnet 128, a release magnet 130 and a private magnet 129. The said private magnet 129, of course, controls the side switch wipers 131, 132, 133 and 134, the said 3 by means of the springs 135 and 136',"and

also of the release magnet through the springs and 137. Thefl-vertical' novement of the switch-shaft, and, therefore, of

the wipers 138, 139 and 140,15 controlledby the vertical magnet 127,while the rotary movementv is controlled by the rotary ma net 128, the rotary magnet circuit being p ovided with v the, usual interrupter spri gs 141. The operative magnets of the switch are, of course, controlled by the subscriber through theuse ofthe vertical and rotary line relays 141-2 and 143, as is well known. Said relays have under their control the usual springs 1 14-, 145 andl lfl. By means of the back-release relay 147 the release of the switch E is brought about after the side switch has passed to third position. Each selector switch in this system is provided with line and private banks.- The contacts of each line bank are adapted to be engaged uby corresponding line wipers such as the wipers 138 and 139,- and the contacts of the private bank by the private wiper 1410. The selector F of the said selector patent. It is a so, of the trunk-release type, and, ther fore, the line relays 1&8 and 149 are connected to the side switch wipers 150 and 151 only while the side switch is in first or second position. It

is a modified form of the selector I is, of cou'rseflalso provided with the vertical magnet152 and the rotary'1nagnet'153, the.re-.

lease magnet 154 and the private magnet 155. The modification fis as. follows: The line relays 1 18 "and 1gl9, as shown, control the so also be seen that since'there is no use I the rotary magnet called trunk-release springs 156 and 157, the

former being connected with the trunk-release conductor 158 andthe latter with the releasemagnet 154. The private magnet in this switch F, unlike the selector E, is not provided with the usual spring that is connected with the release magnet. Furthermore, in this second-selector the bridgecut-off relay and allotted springs are done away with and, therefore, the linerelays 148 and 149 are connected d rectly to"v the nongrounded terminal of the battery. will or normal conductors. such as the normal conductors 261, 262 and 263 allotted to the selector E (Fig. 3), or such as theconduct'ors 343, 344i and 2 16 allotted to the selector E (Fig. 2), these conductors are omitted. The usual shaft wipers 159, 160 and 16.1 are provided for engaging the bank contacts.

The connector switch 1 may also be of any suitable or approved type, and, as shown, is of the type described in said connector patent". The connector switch shaft (not shown), like the first-selector switch shaft, carries the wipers 1'62, 163 and 16 1'. The connectorswitch is also controlled by the calling subscriber tl'l10l1 'l1 the medium= of the-vertical and rotary line relays 165' and 166. The vertical line relay 165 directly controls the vertical magnet 167 and" also 168'. The purpose of the vertical magnet 167 is to give the shaft and shaft wipers their vertical motion, and the rotary magnet 168 imparts to the shaft and shaft wipers a rotary or circular motion. The rotary line relay 166 controls the private magnet 169 which, under certain conditions, in turn controls the vertical and rotary magnets 167 and 168, release magnet 170, and also the side switch-wipers-171, 172, 173 and 174. The side switch 0% the corn nector, like the side switch of the-first-selector, has a normal. or first position, asecond position and a third position. The release magnet is also controlled by the-vertical and-rotary line relays-165 and 166 acting conjointly. This magnet 170 may also be energized through the medium of the bankbridge relays 17 5 and 17 6 by the called subscriber if the calling subscriber doesnot bring about the release of the connector switch. The ringer relay 177, as usual; provides the means whereby the ringer generator M may be bridged across the line 0% the called substation. The central station orsexchange isequipped with busy-signaling ap paratus of any suitable design, comprising an interrupter in series with the primary winding of an induction coil, as'sliown at N, whereby a busy-signaling current is in duced in the secondary winding-178 of the said coil.

The repeater Jcomprises the vertical and rotary line relays 17 9 and 180,21 switching corresponding to.

, ground Gr.

user-see relay 181, by means of which the incoming conductors to the repeater are extended to the condensers 182 and 183 when the repeater conductors are seized by a calling second-selector switch. The relay 1841-, upon energizing, operates to establish a guarding potential at the second-selector banks to pro tect the repeater from being seized when'tlie trunk-line to which the repeater J is allotted is engaged by a subscribercalling into the main exchange from the branch exchange.-

A clearer understanding or theoperatio n of my improved system may be obtainedby considering its action when one subscriber calls another. Assume, for example, that d the subscriber at substation Ai (Fig. 1') de sires to call some subscriber at substation A #2220 (Fig; 3), which is allotted to the main exchange represented in Fig. Since the trunk-lines from the sub-central otlice to the main-central oilice are, in this a, it.

case, arranged to lead on from the tenth level of the connector bank, then when a main exchange connection is desired by sub-exchange subscriber the subscriber must al first call'naught on his dial. To call; naught the subscriber at substation A operates the calling device in the well known manner the digit vnaught:- preliminary impulse for operating the i switch C occurs when the calling subsoils pulls down the dial, whereby the rotary i pulse spring 2 1 is momentarily pressed against theground post 20. its a result, the trip magnet 41'? of the line switch C is energizecl'by a flow of current from ground through the springs 18 and 19, ground 20, rotaryimpulse i line con uctor 32,, ductor 185 bridge cut I A rings 186and the" trip magnet st l thence through the s 1 i, magnet to the conductor 186, differential lay springs 189 68, motor magnet springs 65 and 86, motor magnet 71- to the thence tl'irough battery battery lead 196, to ground Q. As soon as the trip magnet L energizes, the armature 51 is attracted and the plunger as is liberated and thrust into theterminal by a spring 58. When the plunger 44.- engages the bank terminal 6,}; an i M energizing circuit is closed "through the motor'magnet relay 73, which in turn operates to close a circuit through the 'motor magnet 71. The motor magnet operatesto place the idle plungers opposite the first idle bank 129 terminal similar to the terminal The circuit through the relay 73 extends from ground G through the winding 191 of i relay 73, segment 'Zel, wiper arm 75, c 8 conductor 192, bank springs 76 t rough the release magnet 48 to t ry lead 196, thence through bat ihltnough this circuit the release magnet 18, said an n not operatively energize, since the rela wound to a high resistance, while the release magnet is wound to a comparatively low resistance. The relay 73, upon energizing, operates to close the springs 88 and 87 "in contact, whereby a circuit is completed through the motor magnet 71 extending from ground G through the springs 87 and 88, springs 85 and 86, motor magnet 71 to the battery lead 190, thence through battery B to ground G. The motor magnet 71 upon energizing, attracts its armature 81, whereby the pawl 82 engages the ratchet wheel 72 and rotates the said wheel one step. When the armature 81 is attracted against the magnet cores the springs 85 and 86 disengage, thereby breaking the energizing circuit through the motor magnet. The cam-arm 7 6, being in engagement with the pin 77, is operated to advance the plunger shaft 60, and consequently all idle plungers that may be in normal locked position, one step and opposite another bank terminal similar to the bank terminal Q. Also, the Wiper 7 5 is carried from the contact point 84, which cor-- responds to the terminal Q, to the contact point 89, which latter corresponds to the terminal before which the advanced idle plungers are now resting. v

At the instant that the plunger 14 enters the bank terminal Q the following springs are pressed into contact: 63 and 64, 65 and 66, 67 and 68, and 69 and 70. The engagement of the springs 67 and 68 establishes a circuit from ground G by way of the normal conductor 95 to the connector private bank contacts that correspond to the line that terminates in the line switch G, whereby a guarding potential is, established to prevent any subscriber from calling the said line after the calling subscriber at substation A operates his dial preparatory to making a call, as explained. The circuit over which the said guarding potential is established extends from ground G through the bank springs 68 and 67 to the private normal conductor 95, thence to the connector private bank. The engagement of the springs 67 and 68 also closes a circuit through the bridge-cut-oii relay at extending from ground Gr through the springs 68 and 67, conductor 193, through the relay 46 to the battery lead 190, thence through battery B to ground G. The said relay, upon energizing, breaks the contact between the springs 187, 186 and 194, whereby the vertical and rotary line conductors 31 and 32 are disconnected from the trip magnet 47.. The

closure of connection between the springs 89 and establishes a guarding potential at the master switch bank contact 8% over the following circuit: From battery B to the battery lead 190, thence through the release magnet 48 and springs 69 and 70, con-( ductor 192 to the said contact point 84. It will be understood that the bank terminal contact point 117 and into engagement with the contact point 84, upon which latter there is a guarding potential. This guarding potential operates to againenergize the dilferential relay 73, which in turnoperates to again close the energizing circuit for the. motor magnet 71. The current through the said relay flows from the said contact 84 through the wiper to the common segment 74, through the winding 191 of the.

diiierential relay 73 to ground G When the differential relay 7 3 attracts its armature the differential relay springs 87 and 88 are pressed into contact, thereby closing an energizing circuit for the motor magnet 71 from ground G through the said springs 87 and 88, through the springs 85- and 86, motor magnet 71, thence to the battery lead 190, andthrough battery B to ground G.

The motor magnet then operates, as previously explained, to rotate the ratchet wheel 72 one step for advancing the plunger shaft 60 one step, and the master switch wiper 7 5 one step also, andinto engagement with the second segment 89. When thus advanced one step the plunger shaft 60 carries all idle plungers that are in lockedposite the next bank terminal, as explained. If there should be a guarding potential at the bank segment 89 of the master switch bank the differential relay 73 will remain energized, whereby. the energizing circuit through the motor magnet 71 15 again completed when the motor magnet-springs 85 and 86 again engage; and as a result themotor magnet 71 isagain operated, where by the plunger shaft 60 and master switch wiper 75 are advanced another step. This" engagement with the said plunger shaft 'opoperation continues as long as the Wiper 7 5 continues to find segments w th gnardlng potentials. lAs soon as an'idle segment is found, however, the energizing circuit through the differential relay 73 is broken, at which time the said relay in turn breaks the energizing circuit for the motor mag-' net. 71 until the next subscriber makes a call. The closure of connection between the springs 88 and 64. extends the calling subscribers vertical conductor 31 to the yertical trunk conductor 90, which latter leads to the coni'iector vertical line relay 994- The closure 'of contact between the springs 65 and 66 extendst'he subsc'ribers rotary line conductor 32 to the rotary trunk conductor 91, which latter leads to the connector rotary line relay 100.

The subscriber at substation A has thu established connection with the connector H, and now as the dial returns toward normal position, grounding the vertical line conductor 31 each time that the impulse spring 23 is pressed onto the ground post 20, the vertical line relay 99 of" the connector H is energized by a flow of current from the substation ground G and immediately before the dial stops the impulse to'the rotary line conductor 32 energizes the connector rotary line relay 100 also. The circuit through the vertical line relay 99 extends from ground G through the springs ,18 and 19 to the ground post 20, thence through the impulse spring 23 to the vertical line conductor 31, line switch bank springs 63 and 64, vertical trunk line conductor 90, vertical line relay 99 to the battery lead 190, thence through battery 13 to ground G. Each time that the vertical line relay 99 energizes, the relay spring 196 is pressed onto the ground spring 197., The vertical magnet is thereby energized, and the wipers 96, 97 and 98 of the connector are raised one step at a time to the tenth bank level and brought opposite. the first contact of the said level. The energizing circuit of the said magnet extends from ground G through the springs 197 and 196 to the conductor 19S, switching relay springs 199 and 200, private magnet springs 201 and 202, side switch wiper 107, contact point 203, through the vertical magnet 101,

ture of theselector.

thence to battery lead 190, and through battery B to ground G. On the tenth step the arm 204 upon the end of the shaft presses the springs 123 and 124 intoengagement. As previously explained, when the shaft is raised to the tenth level the connector acquires the rotary or automatic selective fea- Therefore, when the rotary impulse energizes the rotary line relay 100, and as a result the private magnet is in turn energized to cause the side switch to pass to second position, the connector automatically rotated. The energizing circuit through the line relay extends from ground G through the springs 18 and 19, ground post 20, rotary impulse spring 24- to the rotary line conductor 32, line switch.- bank springs and 66, trunk conductor 91, rotary line relay 100 to the battery lead 190, thence through battery B to ground G. The rotary line relay, upon energizing, operates to place the springs 207 and 197 in contact, whereby an energizing circuit is closed through the private magnet 103. This circuit extends from ground G through the springs' 197 and 207, switching relay springs 208 and 209, then through the private magnet 103 to the battery lead 190, and through battery B to ground G. The

' tact.

private magnet energizes and permits the side switch to pass to second position. As shown in Fig. 1, the first private contact 210 of the tenth level is grounded. This provision is made in order that the private magnet may be energized at the first rotary step and the side switch tripped to third position as soon as an idle trunk-line is found. If the first set of contacts allotted to the trunk-line is busy the shaft is automatically rotated onto the next set of contacts; also, if the second set of contacts leading to the main exchange is busy the connector shaft wipers are rotated to the next trunk-line. A This automatic rotation is brought about as follows: On the tenth vertical impulse, when the normal arm 20, presses the springs 123 and 124 into contact, an energizing circuit is established through the relay 125 which, upon energizing, operates to press the springs 211 and 212 into contact and to carry the spring 213 from the spring 214 to the spring 215, whereby a new energizing circuit is established through the private magnet 103, said circuit extending frorn'the grounded private bank contact 210 to the shaft wiper 98, side switch wiper 108, contact point 216, through the springs 213 and 215, then through the winding of the private magnet 103, and through battery B to ground G.

When the springs 211 and 212 are pressed into contact, and the side switch passes to second position, an energizing circuit is closed through the rotary magnet 102, extending from ground G through the interrupter 126, springs 211 and 212, contact point 217, side switch wiper 109, through the rotary magnet 102 to the battery lead 190, thence through battery B to ground G. The rotary magnet operates to carry the shaft wipers 96, 97 and 98 onto the first set of contacts of the tenth level, and when the shaft wiper 98 engages the grounded contact point 210 the said private magnet is maintained energized, and the side switch retained iii-second position as long as the wiper 98 engages a busy or grounded conrotary magnet 102 is maintained, and when an idle contact is found the energizing circuit through the private magnet becomes broken and the side switch passes to third position, whereby the energizing circuit through the rotary magnet becomes broken when the side switch wiper 109 leaves the contact point 217. If the first and second This energizing circuit through the.

,subscribers line conductors are extended into connection with the normal conductors 220 and 221,which latter lead to the line switch C allotted to the trunk-line conductors and Furthermore, when the side switch passes to third position a guarding potential is established for protecting the called line. This guarding potential extends from ground G tothe contact point 22%, side switch wiper 108, and shaft wiper98, which latter engages the private contact of the called trunk-line. -The energizing circuit through the cut-oif relay 225 extends from ground G to the private wiper 98, as explained, through the conductor 226, cut-oii relay 225 to the battery lead 190, thence 'through battery B to ground G. The said relay, upon energizing, operates to separate the springs shown in contact in Fig. 1, and to carry the spring 227 into engagement with the spring 228, whereby the vertical normal conductor 220 is extended to the ver tical trunk-line conductor 222. Furthermore, when the side switch wiper 109 passes to third position an energizing circuit is closed through the switching relay 113'. This circuit extends from ground through the normal springs 128 and 124, winding of theswitching relay 113, side switch wiper 109, throi'ighthe winding of the rotary magnet 102 to the battery lead 190, thence through battery B to ground G. Although this circuit includes the rotary magnet 102 the said magnet does not operatively energize, since the relay 113 is wound to a high resistance,

' while the resistance oi the rotary magnet 102 is comparatively low. The relay 113, upon energizing, operates to shift the springs 199 and 208 from the springs 200-and 209 to the springs 229 and 230, whereby the vertical and rotary line relay springs 196 and 207 are connected with the shaft Wipers and 97, respectively. Hence, when the connector vertical and rotary line relays 99 and 100 are energized, thesaid relays operate to deliver or repeat impulses to the line conductors engaged by the shaft wipers 90 and 97. The subscribei"s line conductors 31 and 32 being thus extended to the trunk- 'line conductors 222 and 223, respectively, which terminate in the first-selector switch E of the main or central exchange, the subscriber at substation A is now ready to call anv subscriber of the niaiiieichangc and, therefore; the subscriber-at aubstatien a to when the dial is turned the first time.

which, as stated, is allotted the line #2220 (Fig. 3). Now, to call the number 2220 the dial is turned for each digit, as a result grounding the vertical line conductor 31 a certain number of times and the rotary line conductor once.

It will be understood that each time the dial is turned for a digit a preliminary im pulse is given the rotary line conductor, as-

explained; but the grounding of the rotary line conductor by this preliminary impulse is without effect at this particular time. The preliminary impulse is effective only The first digit being 2 the subscriber at substation A operates the dial accordingly, and the spring 23 is thereby pressed onto the ground post 20 twice. Asa result, the vertical-line relay of the connector H is energized twice by a flow of current from ground G, as previously traced. The connector vertical line relay, upon energizing, operates.

to press the springs'197 and 196 into contact, whereby the ground impulses are repeated to the vertical trunk conductor 222 for energizing the vertical line relay 142 of the firstselector E. Thisenergizing circuit extends from ground G through the connector relay springs 197 and 196, conductor 198, switching relay .springs 199 and 229, -side switch .wiper 105, shaft wiper 96 to the' normal conductor 220, cutoff relay springs 228 and 227 of the line switch C to the vertical trunk-line conductor 222, through the side switch wiper 131, contact point 231 to the vertical line relay 14:2,through the springs of the bridge-cut-o'ff relay 232 to the battery lead 233, thence through battery 1 to ground G. Each time that the vertical line relay 1 1-2 energizes, the line relay spring is pressed onto the ground spring 11%. The vertical magnet 12? is thereby energized and the wipers 138, 139 and 1 10 of the selector E are raised to the second bank level and brought opposite the first contact of said level. The energizing circuit for the said vertical magnet 127 extends from ground (i through the springs ill and 145,

therefore, the rotary line relay 100 of the connector H over a cia lfiiit previously traced. The rotary line relay 100 of the connector in turn operates to place the springs 207 and 197 in contact, whereby the impulse is repeated to the rotary trunk-line conductor 223, and then to the first-selector rotary line relay 113, over a circuit extending from ground G through the springs 197 and 207, switching relay sprai -s 208 and 280, side twitch wiper 10G, shat; wiper 97,'eonduetor 221, rotary trunk-line conductor 223, side switch wiper 132, contact point 23%, rotary line relay 143, through the springs of the cut-elf relay 232 to the battery lead 233, thence through battery B to ground G. Che rotary line relay, upon energizing, presses the line relay spring 146 onto the ground spring-144, thereby establishing a circuit through the private magnet 129 from ground Gr through the springs 1 14. and 146 to the privateemagnet 129, and through the said magnet to battery lead 233, thence through battery B to ground G. The private magnet, upon energizing and decnergizing, permits the selector' side switch to pass from firstto second position, permitting the side switch wipers 133 and-134 to engage the contact points 235 and 236, respectively.

The closureof= connection between the side switch wiper 133 and the contact point 235 sets up an energizing circuit for the rotary magnet 128 from ground-G to the contact'point 235, through the side switch wiper 133, interrupter springs 1 H, rotary magnet 128 to the battery lead 233, and then through battery B to ground G. The said rotary agnet 128 then operates to rotate the wipers 138, 139 and 140 of the selector E into engagement with the first trunloterminalof the second level of the seleetorE, from which terminal, it is assumed, the

trunk-line conductors 237, 238 and 158 lead to the second-selector F. If the first trunk is busy, however, the first private 'bank contact-will be found grounded, and then as soon as the private wiper 140 engages the first grounded priVatebank-contact point,

the private magnet 129 energizes again, locking the side switch in second position. The energizing circuit-for said private mag net extends from the grounded'terminal G of battery B through an occupying switch (not shown) to the private wiper 140, thence through the back-release relay 147 to the side switch wiper 134, contact point 233, private magnet 129, thence through said magnet to the battery lead 233, and through battery B to ground G. The private magnet 129, upon' thus becoming energized, locks the side switch Wiper 133 in engagement with the contact point-235, whereby the rotary magnet 128 will be energized step by step until the Wipers are carried beyond the last busy trunk-line, if, for example, not only the first, but also the second, or still other trunk-lines are busy. Atthe instant that the private wiper leaves the last busy .busy trilnlclines, the'rotary magnet 128 re- "leases the side switch to third position as soon as the wipers are carried into engagement' with the first trunkdine. As soon as the side switch passes to third position, as stated, the subscribers line conductors 31 and are extended to the conductors 237 and238 which, in this case, it is assumed lead to the selector switch F.

the side switch wipers 131 and 132 engage the contact points 240 and 241-1, respectively. Not only is the subscribers line thus on tended, but a guarding potential is established at the private wiper 140, when the side switch wiper 13% passes onto the ground contact point 242, for protecting the seized trunk-lino from interference by other calling SllbSClllOOl'S. tial is established from ground G to the contact point 24.2, thence tl'irough the side switch which 13-1 and through the back-release relay 147 to the private wiper 140. Furthermore, when the selector shaft is given the first vertical step the normal arm 24-3 permits the springs 244- and 245 to engage, whereby an energizing circuit is established through the relay 184 of the repeater J, which relay, in turn operates to establish a giiarding potential at the secondsel ctor bank to protect the repeater J from being seized by a second-selector, thus preventing any subscriber from calling out on the trunk-line conductors 222 and 223, through the repeater J, while the said condoctors are being used by an incoming call.

'The circuit through therelay 184 extends from round G throu h the sorin s 5": h I i'fi and 24 1 conductor 246 sprin s 24'? and it will be seen, of course, that the energizing-circuit for the rotary ma-gnet'128 (to which'reference has already been'made) is destroyed when the idle trunk-line ll seised'th-at is, when the side switch wiper 133 leaves the-contact point The sec ond digit of the number called being 2, the calling subscriber again operates his dial accordingly, as a result grounding the vertical line conductor 31 when the spring 23 meets the ground post 20. conductors 31 and. 32 have been extended to the conductors 23? and 238 (Fig. 2 which lead to the selector F, the vertical and rt The eXtension of the line occurs of course, as soon as 7 This guarding potcn- Since the line tary line relays of the connector H, upon energizing-for the second di it, operate to repeat the second digit impulses to the solcctor switch F in the same manner as the first digit impulses were repeated to the selector' switch E. The vertical line relay 148 of the selector F is, therefore, energized twice by a flow of current from ground G at the connector H to the vertical trunk-line conductor 222, as explained, thence to the side switch wiper 231 of the selector E, con- I tact-point 240, vertical line shaft wiper 138, vertical trunk conductor 237, side switch wiper-150, contact point 253, vertical line relay 1 18 to the battery lead 238, thence through battery B to ground Gthat is, when the vertical line conductor. 31 is grounded for the second digit the vertical line relay 1 1-8 operates to ,close a circuit through the vertical magnet 152, which in turn operates to carry the shaft wipers along step by step and bring them opposite the bank terminals of the second level, as explained in connection with the selector E. When the rotary line conductor 32 is grounded after the vertical impulses, the rotary line relay 149 of the second-selector .F is then, in order, energized by the repeated impulse from the connector H, whereby an energizing circuit is in turn es tablished through the private magnet 155, which private magnet then operates to re; lease the side switch of the selector F, as described in. connection with the selector E, This selector then performs the usual trunk-selecting operation, as before de scribed in connection with selector E; and after the switch F comes to rest the shaft wipers 159 and 166 will be found in engagement with the trunk conductors 254: and 255, respectively, which lead to the connector switch I. At the same time the private wiper 161 establishes a protecting potential at the private contact 256 for guarding the seized trunk-line. When the side switch wipers 150 and 151 engage the contact points and 258 the calling subscribers line con ductors 31 and 32 arestill farther extended to the connector switch I. The round im-- pulses from the substation to the line con--- ductors for the last two digits, namely two and naught, are effective in operating the connector I. For the third digit 2 the ver-. tical impulse sprin 23 is pressed onto the ground post 20 twice, whereby an energizing circuit is each time closed through the connector vertical line relay 1657 The impulses are each time repeated by the vertical line relay of the connector H to the vertical line relay of the connector I, in the same manner in which the impulses are re peated to the selectors E and F. Each time that the vertical line relay 165 of the connectcr I.is energized the line relay springs 259 and 260 are plaessed into contact, there- .by closing an energizing circuit each time through the vertical magnet 167, which lat.

D ter operates in the usual manner, one step line conductor 32 once.

switch passes to third position.

however, are connected with the line conductors 26 1 and 265 which lead to the substation A After the connector shaft has been raised by the vertical impulses the rotary impulse is sent in. This is done when the rotary impulse spring 2 makes contact with the ground post 20, thereby closing an energizing circuit through the rotary line relay .100 0:1 the connector H, and the inrpulse is in turn repeated to the rotary line relay- 166 of the connector I.

The rotary line relay 166, upon energizing, closes an energizing circuit through the private magnet 16), which in turn operates to release the connector side switch from first to second position. The last digit being naught, the calling device is operated aspreviously described, grounding the vertical conductor 31 ten tinies and the rotary The vertical and rotary line relays 165 and 166 are operated as before. However, when the line relay springs 259 and 260 engage, a circuit'is closed through the rotary magnet 168, in-

stead of through the vertical magnet 167.

Each time that the rotary magnet is energized it operates to rotate the shaft and shaft wipers 16:2, 163 and 16 1 one step at a time until the said wipers are carried into engagement with the conductors 261, 262.

and 263- which are allotted to the line of substation A The energizing of the rotary line relay 166, as previously stated,

completes an energizing circuit through the private magnet 169, which now operates with one of two results, namely the release of the side switch from second to third position, thus placing the side switch wipers 171, 172, 173 and 17-1 in contact with their respective contact points of the third position, or the so-called busy-release of the connector. It will first be assumed that the first result (JCCl-lI'S-.--tl1lt is, that the side When the side switch wiper 174 engages the contact point 266 a ground potential is established at the connector bank. The said guarding potential also provides an energizing c1rcuit for the bridge-cut-oti' relay 267 01" the first-selector E thereby removing the bridge formed by the vertical and rotary line relays of the first-selector l To signal the called subscriber the calling subscriber presses the signaling button 87, placing the spring 35 1n (folltflifill with the substation ground G thereby energizing the vertical line relay 99 the connector H, and "in turn the vertical'hne relay of the connector I. The path of the energizing circuit for the relay 99 of the conncctor H extends from ground G through the springs 18 and 19 t the contact point 238, spring 37 springs 33 and 84 to the vertical line conductor 31 trunk conductor 90, vertical relay 99 to the battery lead 190 thence through battery 13 to ground T his relay,

upon energizing, repeats the impulse to tho I 's )l'lX'WS 259 and 260 into contact the rin 'er relay 177 is energized by a low of current from ground to the relay springs 259 and 260, through the private magnet springs, side switch Wiper 173, contact point 268 to the ringer relay 177 and to the battery lead 283, thence through battery 13 to ground G. The ringer relay, upon energ'izing, shifts the springs 269 and 270 from the springs E271 and 272, respectively and onto the springs 27 and 2% respectively This results in. separating the calling subscribers line from the called suhscribcfs line, and in. bridging across the line of the latter the terminals of the ringer generator M. A signaling current is, therefore, sent from the generator M to the ringer relay springs 27 and 269; side switch wiper 1T2, connector shailt wiper H33, normal conductor 262, line cmiductor 265i, condenser 275,

ringer 2'76, spring 277, switch-hook 278 to the vertical line conductor 264- normal conductor Qlil, connector shalt wiper 162, side switch wiper 171, ringer relay springs 270 and 274, back to the generator M.

As Soon as the calling subscriber ceases to press the signaling button 37 the ringer relay 177 hccomcs deenergized, and the springs Q69 and 270 resume their normal position in contact with the springs 271 and 2'52, respectively. In response to the sigrnal the subscriber A removes the rec iver 279 from the switch-hook 5278, thereby re moving the ringer 276 from across his line and bridging: instead the secondary circuit which includes the receiver 279, secondary Winding 280 of the induction-coil 281 and secondary springs and 283. The local transmit er circuit is closed as soon as the springs 28%: and 285 engage" in contact. The two substations A and A are now coi'inected over the circuit shown by heavy lines in Figs. 1, 2- andB, namely: The conductors 26 iand 255st that-called hea the normal conductors 261 and 262, condens ,the vertical. and rotary line rcla cuit through the release relay 1 Elli-l and 365, wipers 155) and ll'iO, side swith wipers 150 and 151, conductors 2 57 and t'll'lflfwi r ers 138 and 139, side, switch Wipers lill and 152 trunk" conductors 92 2 and 1 9, con-- doctors 320 and Q21, wipers 96 and 97 of the connector ll, side switch wipers and. 106 condensers 110 and 111, conductors 90 and 91. bank springs (-34 and 63 on one side and (30 and ($5 on the othcn and the con ductors 31. and of the calling; linev .L Gt release of the central oilice switching rip-- paratus occurs when the calling: suhscriher restores the receiver 2 to the switch-hoot; 2*, thereby pressing the release spring}; '7 El and. so 0 into engagement for a moment The contact of the said release springs grounds the vertical and rotary line conductors 3i 'and 32 Sll'lllllllllllGOllSlY from ground it to the release spring 7, thence through the stain 8 and 9 to the vertical and rotary l ue 100 of the connector ll, which rel:

to in turn ground the trunk-iii n 222 and 223, whereby the vertical line relays and (36 of the co are'cnergized simultaneously, ther ting; the trunk-release springs 5386 contact and thus closing an energria, cuit including the release relay 2855 of "the second-selector F in series with the release magnet or" the connector I. The oath of the circuit extends from ground G to the side switch wiper 28ft release relay $288, sew lcctor shaft wiper lSl connector train-l re lease springs 286 and 28' relea a n'iagnet iii) to the battery lead i333 thence through battery ll to ground G When the connector release i-narjnet 1.70 is thus supplied with cuo rent it energizes; and as a result the switch shaft and side switch are restored to no position, thus breaking the co'nncc tween the connector switch shait a. 163 and 1M and the normal cone 262 and 263, and 'there'fme lTTP'filU" energizing circuits of the ridge-outed 267 of the selector E The baclr relay 288 of the secontlselector l? l the same circuit with the release energizes simultaneously with hi 7 presses the springs 290 and 52% i1. ment which in turn close an or selector E in series with the relea 114- of the second-selector l '1' extends from ground G side switch wip iii-l, through the release relay 147, shat" wiper 14 0, springs 290 and 291', thr h winding; of the release magnet 154i:

e r M to t battery lead thence throug'l'i battery I; to ground G. The release relay 3.4%? ener giaes, and places the springs and 293 in Contact, whereby a circuit is closed. through thesis."atiselectar 5513c Mir Lisa cuit extending from ground through the springs 292 and 298, through the winding of the release magnet 130 to the battery lead 233, thence through battery B to ground G. & The vertical. and rotary line relays of the connector ll, upon energizing, operate to place the trunko'elease springs29a: and. 295 in contact, whereby an energizing circuit is closed through the'releasc magnet 101-, which latter then operates to close a circuit through the release magnet 48 of the line switch 0, said circuit extending from ground. through the spriilgs 295 and 296, conductor 92, bank springs 70 and 69, through the winding of the release magnet 4L8 to the battery lead 190, thence through battery B to ground G. All of the relays andmagnets thus energized attract their, respective armatures and remain energized until the substation release springs 7, 8 and 9 separate and break the ground connection with the line conductors -11 and 32, at which time they all decncrgize, and the remaining unreleased switches are restored. The calling subscriber thus restores all switching apparatus which he originally brought into use. It will be evident that if the calling subscriber neglects to release the-switches the called subscriber (Fig. 3) is unable to operate his switch E as long as the connector switch I remainsconnected tothe line #2220, on account of the cut-off relay 2G7 bein g energized. The back-release is provided in order that called subscribers maynot remain helplessly tied up, so to speak, while this bridge-cutoff relay 267 is energized.

Should the called subscriber desire to make an independent call before the, calling si'ibscriber releases he may do by first 4G breaking the established connection and thus securing control of the first-selector E After establishing connection between the ground springs 296 and 297 he may ground the line conductors 26 and simultaneously by restoring the receiver 279 to the switch-hook 278, and thus pressing the re lease springs 298, 299 and 300 into engagement; As a result an energizing circuit will pass through the vertical back-bridge 5 0 relay 173 and the rotary back-bridge relay 176 of the. connector I. The circuit through the vertical back-bridge relay extends from the substation ground G to the ground springs 296 and 297, to the springs 298' and 2%), vertical conductor 26%, nor nal conductor 261,, shaft wiper 162, side switch wiper 1.71, ringer relay springs 270 and272, vertical back-bridge relay 1'75 to the battery lea d 283., thence through battery B" to so ground Toe energizing circuit of the rotary 'dyg'e relay 1'6 extends from the. release springs 299 1 rotary line conductor 265, i 362. shaft wiper 163, side '2, ringer relay springs 269 herciore; it the calling" subscriber (Fig.

and 271 and rotary back-bridge relay 176 to the battery lead 233, thence through battery 13' to ground G. The back-bridge relays 175 and 176, upon energizing simultaneously, press the back-release springs 301 7 and 302 into contact which completes an energizing circuit to the release magnet 170 from ground to the springs 301 and 302, through the release magnet 1.70, battery lead 238, thence through battery B to ground G. The release magnet is energized and the switch shaft wipers 162, 163 and 16-land side switch are restored to normal position. Theenergizing .circuit" through the bridge-cut-ofi' relay 267 is 30 broken when the shaft wiper 164 leaves the. private bank contact? The connector switch I is thus released and the first-selector E is restored to the control of the substation- .#:2220. lly grounding the line conductors 35 3 and 32 the subscriber-A may restore the remaining switches.

In the preceding it has been explained that when the last rotary impulse comes in the connector switch is liable to be released, or the sideswitch may pass to third position, depending upon the condition of the circuits. It was first assumed-that the side switch had passed to third position, and the explanation was made accordingly. It will now be assumed that the called lineis busy for any reason whatever and, therefore, that the private bank contact allotted to the line is grounded. This being the case, it will be explained how the busy-release of the connector follows at the instant that' the rotary line relay 166 is energized by the aforesaid rotary impulse. The said relayv I 166, upon energizing, energizes the private magnet 169, as previously described, which latter in turn presses the springs 803 and 30-1 into contact. As soon as the said springs 303 and 304C enp'age, the release magnet 170 is placed in connectionwith the priate wiper 16 1; (since the side switch Wiper 0 li-l is now in second position), which wiper 16% has been previously rotated onto a groituided contact. As a result, a flow of current is sent through the release magnet 170 from the grounded private wiper 16 i 115 to the side switch wiper 174:, through the private magnet springs 303 and 304:, to the release magnet 1'70 and to battery lead 233, thence through battery B to ground G. The release magnet 170, upon energizing, releases the connector switch shaft and restores the connector side switch to its'first position, returning the vertical magnet 167 to the controlioi the vertical relay 165.

1} presses the signaling" button 37 and grounds the vertical line conductor 31, he

operates the vertical line relay 165., which latter in turn operates'the vertical magnet 167. Thevertical magnet armature raises 13:3:

ground at the private bank contact that causes the busy-release of: the connector is due to the fact that the called line may be either calling or has been called. in the former case the ground connection is closed by the selector E to the extent that the shaft, upon rising, permits the shaft springs 3G6- and 307 to come into contact. in the latter case--that is, if the called subscriber has been called the ground is supplied by the connector that has made the call in the same manner that has already been explained in connection with the connector 1.

The explanation that has preceded in reference tothe call between the subscriber A. (Fig. 1) and the subscriber A (Fig. refers to a case, as has already been stated, when a subscriber of the exchange indicated in Fig. 1 calls the subscriber of the exchange indicated in Fig. 2, as, for example, where the subscriber A is the subscriber of a private branch exchange and the subscriber A vis a subscriber of the main X- change, the two exchanges being connected by suitable trunk-lines which, in this case, as has been explained, lead oil from the tenth level of the connector switch H. It has already been explained that if any subscriber of the private branch sub-exchange (Fig. 1) Wishes to call any other subscriber of the same'exchange, he may do so by using the connector ll, which connector in that case picks out the'desired line in some level other than the tenth level. This specific arrangement, however, it will be seen, is not essential. To illustrate: W hen the subscriber atsubstation A calls a subscriber of the same local sub-central exchange as the subscriber at substation A on the line #20, 'for'example, the connector H operates in the usual manner'that is, the subscriber controls both the vertical and rotary move- I'ncnts of the switch shaft. To call the number the subscriber at substation A turns the dial for the first digit 2, whereby the trip magnet 47 of the line switch C is energized and operated, as previously explained, to seize an idle. trunk-line leading to a connector switch On the return motion of the dial the Vertical line conductor 31 is grounded twice, thus energizing the vertical line relay 99 twice over circuits already shown. The vertical line relay in turn' closes an energizing circuit throughthe vertical magnet 101, whereby the shaft 'Wipers "96, 07 and 98 are carried two steps in a vertical. direction and brought opposite the bank level in which are located the termi-.

nals of the line Following the vertical impulses the rotary impulse energizes the rotary line relay 100, which in turn operates, as before, to energize the private magnet 103, whereby the side switch may be.

placed in second position. Now, when the vertical line relay 99 operates for: the last digit naught, an energizing circuit is closed through the rotary magnet 102 extendingirom ground (i throughthe springs 197 and g 1%, switching relay springs 199 and- 200, private magnet springs 201 and 202, side switch wiper 107, contact point 309, and through the magnet 102 to the battery lead 190, thence through battery B to ground Gr.

The vertical relay 99 being energized ten tines, the rotary magnet is in turn energized ten times, and the shaft Wipers 96, 97 and 98 are carried into engagement with the bank contacts that constitute the tor-.90

minals of the line #20. 'When the private 1nagnct103 is'energized by the rotary line relay 100 for the last digi one of two results occurs, namely the release of the side switch from sccondto third position, or the 95 so-called lmsy-release of the connector switch if the desired line is busy. It will be assumed that the first result occurs-that is, that the side switch passes to third position. As a result, the side switch wiper 108 0 ground (l. The cut-off relay, upon energiz- 1 ing, places the springs 312 and 313 in contact, whereby the vertical normal conductor 31% is connected with the vertical line conductor 368. T he rotary line conductor 315 is connected with the rotary normal conductor 316.

To signal the called subscriber the subscriber at substation A presses the signaling button 37, whereby the vertical line relay 99 is again energized. Since the side switch 1 has passed to third position the vertical line relay, upon energizing, operates to close a circuit through the ringer relay 112. This circuit extends from ground G through the springs 197 and 196, switching relay springs 199 and 200, private magnet springs 201 and 202, side switch wiper 107, contact point 317, through the ringer relay 112 to the batterv lead 190, thence through battery B to ground G; The ringer relay, upon energiz- 1.

This circuit extends 1 5.

Can

ing, operates, as explained in connection with the ringer relay of the connector 1, to

bridge the ringer generator K across the terminals of the called line for operating the substation ringer 318. substation A, in response to the signal, removes the receiver from the switch-hook. The two substations A and A being connccted over the circuit shown by heavy line conductors in Fig. l, conversation may be carried on. The release of the connector and line switches is brought about when the calling subscriber restores the receiver 2 to the switch-hook 3, thus grounding both 5 line conductors 3-1 and 32 simultaneously and energizing the vertical and rotary lima relays 90 and 100, whereby the release mag net lO-l. becomes energized and, as pointed out operates to close a circuit through the 0 release magnet 48 of the line switch C. The

release magnets 18 and upon energizing, attract their respective arn'iatures and remain in readiness to restore their respective switches when the release springs 7, 8 5 and 9 disengage, thereby removing the ground from the line conductors 3 and 32.

The so-called busy-release of the connector follows as a result of energizing the private magnet for the last digit when the called 9 line is busy. If the called line is busy the private wiper 98 rests on a grounded or protected contact. Now, when'thcprivate magnet 103 is energized for the last-digit the ground potential at the shaft wiper is 5 transmitted to the release magnet 1% over a circuit extendin from the wiper 98 to the side switch wiper 10S, contact point 216 (bearing in mind that the side switch is in second position), through the springs O and 214 to the private magnet spring and to the spring 320, upon the energization of the private magnet, then through the release magnet 104: to the battery lead 190, thence through battery B to ground (-l. 5 The release magnet 1.0%, upon energizing, operates to close the springs 295 and 296 in contact, whereby an energizing circuit is closed through the release magnet 48 of the line switch C. Thus the release of both the connector H and the line switch C is brought about when the connector calls in on a busy line. Thinking that connection has been es tablished the subscriber presses the signaling button 37, thus groundingthe vertical lineconductor 31, whereby an energizing circliit is completed through the trip magnet '47 of the line switch C from the conductor 31, throng-lithe springs 19-4, 186 and 187, winding of the trip magnet 1-7, differential relay springs 189 and 88, through the winding of the motor magnet 71 to the battery lead 190, thence through battery B to ground G. The trip magnet, upon energizing. operates as before to seize anid'le trunk-line leading to a connector switch. as soon as The subscriber at' the line switch operates. the springs 63 and. (3st engage, thereby extending the ground connection of the vertical line conductor 31 to the trunk conductor 90, and then through the connector vertical line relay 99 which operates to close a circuit through the rertical magnet 101. The connector shaft is raised one step and the normal arm permits the s irings 121 and. 12-2 to engage, thus coni'iei'zting the busy-signaling machine L with the side switch wiper 106 which is now in first position. Upon hearing the busy-signal the calhng subscriber will understand that the desired hneis busy and will res ore the switching apparatus by J lead off from the fifth'level of the senondselector banks, and thaththe conduetors 34:3

and 344; leading from the repeater are connected in multiple with the firstseleetor E to the same trunk-line, which. trunk-line tor minates in the brivate branch or 'siibrentral exchange (Fig. 1). It will be evident that from the said fifth level of the secondselectors tenrepeaters J may be reachechand, therefore ten different trunk-lines to thee change'shown in Fig. 1. As explained the firstselector is used when a. call is made into the main exchange from the subcentral. exchange; but when a call goes from the main exchange to the sub-central the repeater J" is called into service instead. hen the repeater J is called into service the selector E is put out of service, and when the selector E is called into service the repeater J is put out of service, in order to prevent interfere ence. These points will be better understood atter the method of making calls has been fully explained. It will also be apparent that in. order to call any subscril'ier at the exchange shown in Fig. 1 from the inain'exchange, the prefix must be given to every number of said exchange. For example: Assume that thesubscriber at sub-, station A of the main exchange (Fig. 2) desires to call the subscriber atsuhstation A (Fig. 1), the number of which is 20, as already stated. in that event the subscriber .at sul'istation A? must first turn his dial for 'intoengagement with the terminals of an idle tri'lnlr line leading to a second-selector 

